nginx auth_request fails with ‘upstream timed out’

I’m writing a simple reverse proxy to exchange a JWT for an API while connecting to a VOD service (livepeer). Testing on my machine, using docker.

But the request always hangs. Here’s the nginx.conf:

events {
}

http {
    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    access_log  /dev/stdout;
    error_log  /dev/stdout;

    server {

        listen 8080;

        server_name creators_proxy;

        location /api {
            auth_request /auth;
            proxy_set_header Authorization 'Bearer here_goes_the_key';
            proxy_pass https://livepeer.studio/api;
        }

        location = /auth {
            internal;
            proxy_pass here_goes_auth_url;
        }

        location = /auth2 {
            proxy_pass here_goes_auth_url;
        }
    }
}

and the dockerfile:

# Use the official NGINX image as a parent image
FROM nginx:latest

COPY nginx.conf /etc/nginx/nginx.conf

I build the container with docker run -d --name docker-nginx -p 8080:8080 -v ./nginx.conf:/etc/nginx/nginx.conf -d nginx_img

And call http://localhost:8080/api/asset/request-upload

The auth_url is from pipedream, to inspect the request going out. But the request never lands. I get:

upstream timed out (110: Connection timed out) while reading response header from upstream, client: 172.17.0.1, server: creators_proxy, request: "POST /api/asset/request-upload HTTP/1.1", subrequest: "/auth", upstream: "https://xx.xxx.xx.xx:443/auth", host: "localhost:8080"

What I’ve tried so far:

1. curl‘d the auth url from my machine (it works)
2. curl‘d the auth url from the docker instance (it works)
3. Called location /auth2 to go directly to the auth_url (it works)
4. Checked whether this nginx version has the auth_request module enabled (it has)
5. Commented out the auth_requestin the /api location (doesn’t hang)

Any ideas?